Ask McDonald’s about the wisdom of challenging consumers to tweet #McDStories or Qantas about the trouble it got into with its #QantasLuxury competition and you’ll discover that if social media really is a conversation, it’s often an unpleasant one in which gangs of consumers surround and abuse a brand that is simply trying to engage in some light banter.

The most recent instalment is the already infamous #WaitroseReasons campaign. It started, as it usually does, with an inane attempt to find something – anything – to drive Twitter conversations about the brand. I am not sure what the social media people at Waitrose were expecting when they asked consumers to complete the sentence “I love shopping at Waitrose because…” – “I love your oranges”?, “Aisle 5 is excellent”? – but whatever it was, it certainly wasn’t what started to shoot out from Twitter..

One punter claimed to shop at Waitrose because he hated poor people, another because his “butler had the week off”. Another suggested he shopped there because “Clarissa’s pony just will NOT eat ASDA straw”, while another favoured Waitrose because “food must automatically be better if it costs three times as much”. On and on it went. First on Twitter and later replayed across most of Britain’s main media sites. A stream of unadulterated anti-brand statements, all at Waitrose’s expense.

But that isn’t the story this week. The really remarkable thing is what happened in the marketing community as the campaign wheeled off on its rapid parabola of brand damage. One might have expected marketers to point out the mistake Waitrose had made and discuss the risks of using Twitter. But this is social media we are talking about – the tool that can do no wrong. So most marketers either dismissed the campaign as being a bit of humour that would do the brand no harm or, even more astonishingly, claimed that #WaitroseReasons was an enormous branding success. Jason Woodford, for example, chief executive at digital marketing agency SiteVisibility, claimed the campaign was a “very clever marketing ploy from Waitrose” that had “reinforced its brand values of quality and reliably excellent service as a key point of differentiation from the other grocery chains”. Is he insane?

Others agreed with Woodford’s bonkers diagnosis, pointing out that Waitrose’s campaign “has certainly not damaged its reputation” and concluding that “the argument that Waitrose has come out on top with this campaign is entirely persuasive.” Are these people serious?

Our readers at Marketing Week were little better. The comments under Sebastian Joseph’s (excellent) analysis of the situation proved another damning indictment of current marketing thinking and the degree to which most have been drinking the social media Kool Aid. Of the eight comments posted by the time of writing this column, only one agreed that the Waitrose campaign had been botched, with the other seven concluding that the error was either painless or actually a success.

Let’s be clear on what happened last week for the sake of our discipline and the minority of us left working in it who have not lost our marbles to social media. The ultimate purpose of Waitrose’s social media strategy is not to start conversations or increase the number of followers the brand has on Twitter. The purpose of Waitrose’s social media strategy is to build its brand and increase sales. Waitrose has had a successful strategy to do just that, built around two approaches – first, getting existing shoppers to shop more frequently at Waitrose and second, attracting new shoppers into the stores.

But this campaign inadvertently positions the supermarket as posh, snobby, overpriced and reserved exclusively for the upper classes. That’s terrible news for Waitrose, because it has spent the past four years positioning its brand away from these stereotypes and towards a more accessible, value-based position to drive market share gains. Much of that good work has been undermined by a single, ill-conceived Twitter campaign aimed at 30,000 followers, but now processed by millions.

Existing shoppers at Waitrose, the middle-class segment it targets, will feel sensitive and perhaps a little less enthusiastic about entering the store now, and store traffic will decline. Potential converts to Waitrose will have had their stereotypes confirmed and be less likely to consider the switch in future. Perhaps neither of these impacts will be huge, but they will be negative and they were self-inflicted.

Social media certainly offers brands interesting new tactical opportunities, but it does not reverse the laws of marketing reality. A bad idea is still a bad idea. A crap campaign remains crap. And a message seen by millions that contradicts a company’s stated marketing strategy and links the brand with negative associations is a failure, no matter what medium it is delivered through.

And if some marketers cannot see this because they view all things through the rose-coloured spectacles of social media, I worry for them and the discipline they work within.